wms - Need clarification on GeoServer Meta-tile

GeoServer WMS meta-tile is often recommended to be used to overcome problems such as:

• point symbols close to tile edges are cut


• labels are duplicated

I just need some clarification here: WMS meta-tile does not completely guarantee that such problems gone. WMS meta-tile only reduces them. Hence, in term of point symbols, symbols close to tile edges are still cutted but the occurrence of this is much reduced.

Is it right?

Answer

You are right that metatiles alone do not prevent cutting the symbols. In the picture below with 3x3 metatiles the inner star symbol will not be cut but the outer will because it is on the border of the metatile.

With symbols you can get a perfect result by using "gutter" parameter with a value that is bigger than half of the size of the biggest symbol. Read the usage from http://docs.geoserver.org/2.8.x/en/user/webadmin/tilecache/defaults.html

The gutter size sets the amount of extra space (in pixels) used when generating a tile. Use this in conjunction with metatiles to reduce problems with labels and features not being rendered incorrectly due to being on a tile boundary.

Labels are harder to handle because they might require very big gutter value and then double labels may appear because of automatic placement of labels.